# Making Serial Port Drivers User-Configurable

This topic explains how to set up a serial driver so that it can be end-user configured (via parameters) to run on any of a flight controller board's configurable serial ports.

## Preconditions

The driver is assumed to already exist, and be started in the shell using the command syntax:
```sh
<driver_name> start -d <serial_port> [-b <baudrate> | -b p:<param_name>]
```
where,
- `-d`: serial port name.
- `-b`: Baud rate (optional) if the driver supports multiple baud rates. If supported, the driver must allow you to specify the rate as both a bare baudrate and as a parameter name in the form `-b p:<param_name>` (which can be parsed with `px4_get_parameter_value()`). :::tip See the [gps driver](https://github.com/PX4/PX4-Autopilot/blob/main/src/drivers/gps/gps.cpp#L1023) for an example.
:::


## Making the Driver Configurable

To make driver configurable:
1. Create a YAML module configuration file:
   - Add a new file in the driver's source directory named **module.yaml**
   - Insert the following text and adjust as needed:
     ```
     module_name: uLanding Radar
     serial_config:
         - command: ulanding_radar start -d ${SERIAL_DEV} -b p:${BAUD_PARAM}
           port_config_param:
             name: SENS_ULAND_CFG
             group: Sensors
     ```
:::note
The full documentation of the module configuration file can be found in the [validation/module_schema.yaml](https://github.com/PX4/PX4-Autopilot/blob/main/validation/module_schema.yaml) file. This is also used to validate all configuration files in CI.
:::
1. Add the module configuration to the **CMakeLists.txt** file for the driver module:
   ```
   px4_add_module(
    MODULE drivers__ulanding
    MAIN ulanding_radar
    SRCS
        ulanding.cpp
    MODULE_CONFIG
        module.yaml
    )
   ```

